Liquid crystal composition

ABSTRACT

A liquid crystal composition is disclosed. The liquid crystal composition includes a negative nematic liquid crystal, a positive nematic liquid crystal, and a ferroelectric liquid crystal.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC §119 to Korean Patent Application Nos. 10-2012-0067984, filed on Jun. 25, 2012, and 10-2012-0118692, filed on Oct. 24, 2012, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Field

The present disclosure herein relates to a liquid crystal composition, and more particularly, to a liquid crystal composition including a nematic liquid crystal and a ferroelectric liquid crystal.

2. Description of the Related Art

A liquid crystal display device is one of the most widely used flat panel display devices, and researches on achieving a device having a high definition, a light luminance and a large-size have been actively conducted. As a part of the researches, the structure of electrodes in a liquid crystal display device becomes diverse and complicated to achieve the high definition, the high luminance and the large-size of the liquid crystal display device. When a driving voltage is applied to the electrodes, the alignment of liquid crystal molecules in a liquid crystal layer may be changed. However, the alignment of the liquid crystal molecules may be non-uniform and unstable due to the diverse and complicated electrodes. The non-uniform and the unstable alignment of the liquid crystal molecules may deteriorate the luminance of the liquid crystal display device.

SUMMARY

The present disclosure provides a liquid crystal composition having a uniform and stable alignment state.

The object of the present inventive concept should not be construed as limited to the object set forth herein. Rather, other objects not set forth herein will be precisely understood to those skilled in the art from the following.

Embodiments of the inventive concept provide a liquid crystal composition. The composition includes a negative nematic liquid crystal, a positive nematic liquid crystal, and a ferroelectric liquid crystal.

In some embodiments, the liquid crystal composition may include about 70 to about 99.9 wt % of the negative nematic liquid crystal and about 0.1 to about 30 wt % of a mixture of the positive nematic liquid crystal and a remaining amount of the ferroelectric liquid crystal.

In other embodiments, an amount of the ferroelectric liquid crystal may be about 10 to about 99 wt % based on the mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal.

In still other embodiments, the liquid crystal composition may further include a reactive mesogen material.

In even other embodiments, the liquid crystal composition may include about 0.1 to about 30 wt % of the mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal, about 0.01 to about 3 wt % of the reactive mesogen material and a remaining amount of the negative nematic liquid crystal.

In yet other embodiments, the negative nematic liquid crystal may include nematic liquid crystal molecules.

In further embodiments, the negative nematic liquid crystal may further include first base liquid crystal molecules. Each of the first base liquid crystal molecules may include at least one selected from the group consisting of a negative nematic liquid crystal molecule, a positive nematic liquid crystal molecule, and a neutral liquid crystal molecule.

In still further embodiments, the negative nematic liquid crystal molecules may include a first negative nematic liquid crystal molecule having a first negative dielectric anisotropy and a second negative nematic liquid crystal molecule having a second negative dielectric anisotropy different from the first negative dielectric anisotropy.

In even further embodiments, the positive nematic liquid crystal may include nematic liquid crystal molecules.

In yet further embodiments, the positive nematic liquid crystal may further include second base liquid crystal molecules. Each of the second base liquid crystal molecules may include at least one selected from the group consisting of a negative nematic liquid crystal molecule, a positive nematic liquid crystal molecule, and a neutral liquid crystal molecule.

In much further embodiments, the positive nematic liquid crystal molecules may include a first positive nematic liquid crystal molecule having a first positive dielectric anisotropy and a second positive nematic liquid crystal molecule having a second positive dielectric anisotropy different from the first positive dielectric anisotropy.

In still much further embodiments, the ferroelectric liquid crystal may further include ferroelectric liquid crystal molecules.

In even much further embodiments, the ferroelectric liquid crystal may further include third base liquid crystal molecules. Each of the third base liquid crystal molecules may include at least one selected from the group consisting of a negative nematic liquid crystal molecule, a positive nematic liquid crystal molecule, and a neutral liquid crystal molecule.

In yet much further embodiments, the ferroelectric liquid crystal molecules may include a first ferroelectric liquid crystal molecule and a second ferroelectric liquid crystal molecule different from the first ferroelectric liquid crystal molecule.

In other embodiments of the inventive concept, a liquid crystal composition is provided including a non-ferroelectric liquid crystal and a ferroelectric liquid crystal.

In some embodiments, the liquid crystal composition may include about 0.1 to about 30 wt % of the ferroelectric liquid crystal.

In other embodiments, the non-ferroelectric liquid crystal may include a negative nematic liquid crystal and a positive nematic liquid crystal.

In still other embodiments, the non-ferroelectric liquid crystal may include a negative nematic liquid crystal.

In even other embodiments, the liquid crystal composition may include about 70 to about 99.9 wt % of the negative nematic liquid crystal and about 0.1 to about 30 wt % of the ferroelectric liquid crystal.

In yet other embodiments, the liquid crystal composition may further include a reactive mesogen material.

In further embodiments, the liquid crystal composition may include about 0.1 to about 30 wt % of the ferroelectric liquid crystal, about 0.01 to about 3 wt % of the reactive mesogen material and a remaining amount of the negative nematic liquid crystal.

According to the present inventive concept, a liquid crystal composition may include a positive nematic liquid crystal, a negative nematic liquid crystal, and a ferroelectric liquid crystal. In a liquid crystal display device including the liquid crystal composition, the alignment uniformity and the stability of liquid crystal molecules in the liquid crystal composition may be increased and the luminance of the liquid crystal display device may be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the inventive concept, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the inventive concept and, together with the description, serve to explain principles of the inventive concept. In the drawings:

FIG. 1 is a graph illustrating an electric characteristic of a liquid crystal composition in accordance with an example embodiment;

FIG. 2 is a cross-sectional view for explain a liquid crystal display device in accordance with an example embodiment;

FIG. 3 is a plan view for explaining slit phenomenon of electrodes in accordance with example embodiments;

FIGS. 4A to 4E are graphs illustrating the transmittance of liquid crystal display devices in accordance with Examples 1 to 4 and Comparative Examples 1 to 3;

FIGS. 5A to 5D are graphs illustrating the response time of liquid crystal display devices in accordance with Examples 1 to 4 and Comparative Examples 1 to 3;

FIG. 6A is a graph illustrating the transmittance of liquid crystal display devices in accordance with Examples 5 to 8, and FIG. 6B is a graph illustrating the response time of liquid crystal display devices in accordance with Examples 5 to 8;

FIGS. 7A to 7C and FIGS. 8A to 8C are the textures of liquid crystal display devices in accordance with Comparative Example 1, Examples 3 and Example 9; and

FIGS. 9A and 9B are graphs illustrating the gray level of the textures in FIGS. 7A, 7B, 8A and 8B.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Example embodiments of the inventive concept will be described below in more detail with reference to the accompanying drawings. The inventive concept may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this description will be thorough and complete, and will fully convey the scope of the present inventive concept to those skilled in the art.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present inventive concept. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, and/or devices, but do not preclude the presence or addition of one or more other features, steps, operations, and/or devices thereof.

It will also be understood that when a layer (or film) is referred to as being ‘on’ another layer (or film) or substrate, it can be directly on the other layer (or film) or substrate, or intervening layers (or films) may also be present.

It will be understood that, although the terms first, second, third etc. may be used herein to describe various regions, layers (or films), etc. these regions and layers should not be limited by these terms. These terms are only used to distinguish one region or layer (or film) from another region or layer (film). Thus, a first layer discussed below could be termed a second layer. Example embodiments embodied and described herein may include complementary example embodiments thereof. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive concept belongs.

It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Hereinafter, example embodiments will be described in detail with reference to the accompanying drawings.

Liquid Crystal Composition First Embodiment

The liquid crystal composition according to embodiments of the inventive concept may include a negative nematic liquid crystal having a negative dielectric anisotropy, a positive nematic liquid crystal having a positive dielectric anisotropy and a ferroelectric liquid crystal.

In some embodiments, the liquid crystal composition may include about 70 wt % to about 99.9 wt % of the negative nematic liquid crystal. The liquid crystal composition may further include about 0.1 wt % to about 30 wt % of the mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal.

The mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal may include about 1 wt % to about 90 wt % of the positive nematic liquid crystal and about 10 wt % to about 99 wt % of the ferroelectric liquid crystal.

In some embodiments, the ferroelectric liquid crystal in the liquid crystal composition may be in a range of about 0.01 wt % to about 29.7 wt %. When the amount of the ferroelectric liquid crystal is about 0.01 wt % or less of the liquid crystal composition, the liquid crystal alignment of the liquid crystal composition may be unstable. When the ferroelectric liquid crystal in the liquid crystal composition exceeds about 29.7 wt % of the total amount of the liquid crystal composition, the viscosity of the liquid crystal composition may be increased and the response time of a display device including the liquid crystal composition may be decreased. Preferably, the amount of the ferroelectric liquid crystal in the liquid crystal composition may be about 10 wt % based on the total amount of the liquid crystal composition.

Hereinafter, exemplary materials on the negative nematic liquid crystal, the positive nematic liquid crystal and the ferroelectric liquid crystal may be explained. However, the negative nematic liquid crystal, the positive nematic liquid crystal and the ferroelectric liquid crystal may not be limited to the following embodiments in the present inventive concept.

The characteristic of a nematic liquid crystal will be explained in brief, and then, example embodiments of the negative nematic liquid crystal and the positive nematic liquid crystal will be classified.

Nematic liquid crystal is referred to as a liquid crystal having long and thin molecules with irregular positions to each other but with a specific longitudinal arrangement of the molecules. The longitudinal axis of each molecule of the nematic liquid crystal may move freely, and the nematic liquid crystal may have a low viscosity and may easily flow. Since the up and down of the nematic molecules are substantially the same, the polarity of the liquid crystal may be offset. Thus, the nematic molecules generally do not illustrate the ferroelectricity. The physical properties along the molecular axis direction and the vertical direction of the liquid crystal may be quite different. Therefore, the nematic liquid crystal may be a material having an optical anisotropy. When a dielectricity difference (Δ∈) between the dielectricity in parallel to the molecular axis and the dielectricity vertical to the molecular axis is less than 0, the liquid crystal is referred to as the negative nematic liquid crystal, and when the dielectricity difference (Δ∈) is greater than 0, the liquid crystal is referred to as the positive nematic liquid crystal.

Negative Mematic Liquid Crystal

In some embodiments, the negative nematic liquid crystal may include negative nematic liquid crystal molecules. In one aspect, the negative nematic liquid crystal molecules may be single molecules. In other aspects, the negative nematic liquid crystal molecules may be a mixture of different materials. For example, the negative nematic liquid crystal molecules may include first negative liquid crystal molecules having a first dielectricity and second negative liquid crystal molecules having a second dielectricity. In this case, the first dielectricity may be different from the second dielectricity.

In other embodiments, the negative nematic liquid crystal may include negative nematic liquid crystal molecules and first base liquid crystal molecules. Each of the first base liquid crystal molecules may include at least one selected from the group consisting of a negative liquid crystal molecule having a negative dielectric anisotropy, a positive liquid crystal molecule having a positive dielectric anisotropy and a neutral liquid crystal molecule. In one aspect, the negative nematic liquid crystal may include c liquid crystal molecules having one kind of negative dielectric anisotropy and the first base molecules. In other aspects, the negative nematic liquid crystal may include liquid crystal molecules having diverse negative dielectric anisotropies and the first base liquid crystal molecules.

Hereinafter, examples on the negative nematic liquid crystal will be embodied and explained. The following materials may be used alone or as a mixture thereof.

The negative nematic liquid crystal may include a halogen group, a cyanide group or an isocyanate group nematic liquid crystal. The negative nematic liquid crystal may include a halogen group, a cyanide group or an isocyanate group negative nematic liquid crystal alone or as a mixture thereof. In addition, the negative nematic liquid crystal may further include the first base liquid crystal molecules.

The halogen group negative nematic liquid crystal may include a fluorine group, a chlorine group or a bromine group material, and may have a monocyclic or polycyclic structure.

The halogen group negative nematic liquid crystal and a dicyclic structure may be represented by following Chemical Formulae 1 and 2.

In Chemical Formulae 1 and 2, R represents an alkyl or an alkoxy group having 1 to 15 carbon atoms (in which, hydrogen may be substituted with CN, CF₃ or a halogen, and —CH₂— group may be substituted with —CH═CH—, —O—, —CO—, —COO—, —OOC—, —O—OC—O— or —S—), X independently represents a halogen, a halogenated alkyl, a halogenated alkoxy, a halogenated alkenyl or a halogenated alkenyloxy having 1 to 15 carbon atoms, and L¹ and L² are independently represents hydrogen or a halogen.

The halogen group negative nematic liquid crystal and a tricyclic structure may be represented by following Chemical Formulae 3 through 6.

In Chemical Formulae 3 to 6, R, L¹ and L² represents the same meaning as defined in Chemical Formulae 1 and 2, L³ and L⁴ independently represents hydrogen or a halogen, Z represents a single bond, —CF₂O—, —OCF₂—, —COO—, —O—CO—, —CH₂CH₂—, —CH═CH—, —C≡C—, —CH₂O—, —(CH₂)₄—, CF═CF—, —CH═CF— or —CF═CH—.

The halogen group negative nematic liquid crystal and a tetracyclic structure may be represented by following Chemical Formulae 7 to 9.

In Chemical Formulae 7 to 9, Y represents hydrogen or a halogen, R¹ represents an alkyl or an alkenyl having 1 to 15 carbon atoms, R² represents an alkyl, an alkenyl or an alkoxy having 1 to 15 carbon atoms (in R¹ and R², hydrogen may be substituted with CN, CF₃, or a halogen atom, and CH₂ group may be substituted with —O—, —S—, —C≡C—, —CH═CH—, —OC—O— or —O—OO—), Z represents a single bond, —CF₂O—, —OCF₂—, —COO—, —O—OO—, —CH₂CH₂—, —CH═CH—, —C≡C—, —CH₂O—, —(CH₂)₄—, CF═CF—, —CH═CF— or —CF═CH—.

The halogen group negative nematic liquid crystal may include a fluorinated indane derivative at the side portion and may be represented by following Chemical Formula 10.

In Chemical Formula 10, m represents an integer and n represents 0 or 1.

The cyanide group negative nematic liquid crystal may be represented by following Chemical Formulae 11 to 13.

In Chemical Formulae 11 to 13, R³ represents an alkyl group having 1 to 15 carbon atoms (in which, hydrogen may be unsubstituted or at least monosubstituted with CN, CF₃ or a halogen, and CH₂ group may be replaced with —O—, —S—, —C≡C—, —CH═CH—, —OC—O— or —O—CO—), L¹ and L² independently represents hydrogen or a halogen, Z represents a single bond, —CF₂O—, —OCF₂—, —COO—, —O—CO—, —CH₂CH₂—, —CH═CH—, —C≡C—, —CH₂O—, —(CH₂)₄—CF═CF—, —CH═CF— or —CF═CH—.

The negative nematic liquid crystal may be a single material or a mixture. In some embodiments, the negative nematic liquid crystal mixture may include,

(a) a liquid crystal component A including at least one compound having a dielectric anisotropy of −1.5 or less;

(b) a liquid crystal component B including at least one compound having a dielectric anisotropy of from −1.5 to +1.5; and

(c) a chiral component C.

The liquid crystal component A may include at least one among the compounds represented by following Chemical Formulae 14 to 17.

The liquid crystal component B may include at least one among the compounds represented by following Chemical Formulae 18 to 20. The liquid crystal component B may be the first base liquid crystal molecules.

In Chemical Formulae 14 to 20, R⁴ and R⁵ independently represents an alkyl, an alkoxy, an alkoxy alkyl, an alkenyl or an alkenyl oxy having 1 to 15 carbon atoms (in which, hydrogen may be substituted with CN, CF₃, or a halogen atom, and —CH₂— group may be substituted with —CH═CH—, —O—, —CO—, —COO—, —OOC—, —O—OC—O— or —S—), and Y¹ represents hydrogen or a halogen.

The chiral component C may include a plurality of dopants as follows. The selection of the dopant may be insignificant.

Positive Nematic Liquid Crystal

In some embodiments, the positive nematic liquid crystal may include positive nematic liquid crystal molecules. In one aspect, the positive nematic liquid crystal molecules may be single molecules. In other aspects, the positive nematic liquid crystal molecules may be a mixture of different materials. For example, the positive nematic liquid crystal molecules may include first positive liquid crystal molecules having the positive dielectric anisotropy having a first dielectricity and second positive liquid crystal molecules having the positive dielectric anisotropy having a second dielectricity. In this case, the first dielectricity may be different from the second dielectricity.

In other embodiments, the positive nematic liquid crystal may include positive nematic liquid crystal molecules and second base liquid crystal molecules. Each of the second base liquid crystal molecules may include at least one selected from the group consisting of a liquid crystal molecule having a negative dielectric anisotropy, a liquid crystal molecule having a positive dielectric anisotropy and a neutral liquid crystal molecule. In one aspect, the positive nematic liquid crystal may include positive nematic liquid crystal molecules having one kind of positive dielectric anisotropy and the second base molecules. In other aspects, the positive nematic liquid crystal may include liquid crystal molecules having diverse positive dielectric anisotropies and the second base liquid crystal molecules.

Hereinafter, examples on the positive nematic liquid crystal may be embodied and explained. The following materials may be used alone or as a mixture thereof.

The positive nematic liquid crystal may include a cyanide group, an isocyanate group or a halogen group positive nematic liquid crystal. The positive nematic liquid crystal may include a cyanide group, an isocyanate group or a halogen group positive nematic liquid crystal alone or as a mixture thereof. In addition, the positive nematic liquid crystal may further include the second base liquid crystal molecules.

The cyanide group positive nematic liquid crystal may have a dicyclic structure or a tricyclic structure.

The cyanide group positive nematic liquid crystal having the dicyclic structure may be represented by following Chemical Formula 21.

In Chemical Formula 21, R⁶ represents an alkenyl having 1 to 15 carbon atoms (in which, hydrogen may be substituted with CN, CF₃ or a halogen, and —CH₂— group may be optionally substituted with —CH═CH—, —O—, —CO—, —COO—, —OOC—, —O—OC—O— or —S—). Particular examples of Chemical Formula 21 are as follows.

In Chemical Formula 21, R⁷ represents H, CH₃, C₂H₅ or n-C₃H₇.

The positive nematic liquid crystal having the tricyclic structure may be represented by following Chemical Formula 22.

R³ represents an alkyl group having less than 15 carbon atoms and unsubstituted or at least monosubstituted with CN, CF₃ or a halogen, as defined in Chemical Formulae 11 to 13, in which, at least one CH₂ group of the alkyl group may be replaced with —O—, —S—, —C≡C—, —CH═CH—, —OC—O— or —O—CO—, and L¹ and L² independently represents hydrogen or a halogen.

The isocyanate group positive nematic liquid crystal may be represented by following Chemical Formula 23.

In Chemical Formula 23, R⁸ represents C_(n)H_(2n+1)O, C_(n)H_(2n+1), or C_(n)H_(2n−1), in which, n represents 1 to 15, A represents

B represents —CH₂—CH₂— or —C≡C—, X¹ represents hydrogen or a halogen, and m represents 1, 2, 3 or 4. Particular examples on Chemical Formula 23 are as follows.

The halogen group positive nematic liquid crystal may include a fluorine group material or a chlorine group material, and may have a monocyclic structure or a polycyclic structure. The fluorine group positive nematic liquid crystal may be represented by following Chemical Formulae 24 to 27.

In Chemical Formulae 24 to 27, R⁹ and R¹⁰

represents an alkyl, an alkoxy, a fluorinated alkyl, a fluorinated alkoxy, an alkenyl, an alkenyloxy, an alkoxy alkyl or a fluorinated alkenyl having 1 to 15 carbon atoms, L²¹, L²², L²³, and L²⁴ independently represents hydrogen or a fluorine, and Z represents a single bond, —CF₂O—, —OCF₂—, —COO—, —O—CO—, —CH₂CH₂—, —CH═CH—, —C≡C—, —CH₂O—, —(CH₂)₄—, CF═CF—, —CH═CF— or —CF═CH—.

The halogen group positive nematic liquid crystal having a dicyclic structure may be represented by following Chemical Formula 28.

In Chemical Formula 28, R¹¹ represents hydrogen, a halogen, or an alkenyl, an alkenyloxy, an alkenyloxy, an alkynyl or an alkynoxy having 1 to 15 carbon atoms, in R¹¹, at least one —CH₂— group may be substituted with —O—, C═O or —S—, L⁵ represents a halogen, a fluorinated alkyl, a fluorinated alkoxy, a fluorinated alkenyl, an alkenyloxy or an oxyalkyl having 1 to 15 carbon atoms, —OCF₃, —OCHFCF₃ or SF₅, L⁶, L⁷, L⁸ and L⁹ independently represents hydrogen or a halogen, and Z represents a single bond, —CF₂O—, —OCF₂—, —COO—, —O—CO—, —CH₂CH₂—, —CH═CH—, —C≡C—, —CH₂O—, —(CH₂)₄—, CF═CF—, —CH═CF— or —CF═CH—. Particular examples of Chemical Formula 28 are as follows.

In the above structures, n represents 1 to 15.

The halogen group positive nematic liquid crystal having the tricyclic structure may be represented by Chemical Formulae 29 to 33.

In Chemical Formulae 29 to 33, R¹² represents an alkyl or an alkenyl having 1 to 15 carbon atoms (in which, the alkyl or the alkenyl may be unsubstituted, or at least monosubstituted with CN, CF₃, or a halogen, and at least one of —CH₂— group may be substituted with —O—), and X³ represents —F, —Cl, —OCF₃, —OCHF₂, —OCH₂F or —CF₃. Particular examples of Chemical Formula 29 are as follows.

In the above structures, R¹² represents the same as defined above.

The halogen group positive nematic liquid crystal having a tetracyclic structure may be represented by following Chemical Formulae 34 to 36.

In Chemical Formulae 34 to 36, R¹³ independently represents an alkyl, an alkoxy, or an alkenyl having 1 to 15 carbon atoms (in the alkyl, alkoxy or alkenyl, hydrogen may be substituted with CN, CF₃, or a halogen, and —CH₂— group may be substituted with —CH═CH—, —O—, —CO—, —COO—, —OOC—, —O—OC—O— or —S—), and Z represents a single bond, —CF₂O—, —OCF₂—, —COO—, —O—CO—, —CH₂CH₂—, —CH═CH—, —C≡C—, —CH₂O—, —(CH₂)₄—, CF═CF—, —CH═CF— or —CF═CH—.

The positive nematic liquid crystal having trisubstituted fluorine or cyanide groups may be represented by following Chemical Formula 37.

In Chemical Formula 37, at least one among two of R¹⁴ and R¹⁵ may be an alkenyl group having less than 15 carbon atoms unsubstituted or at least monosubstituted with CN, CF₃ or a halogen, the other one among two of R¹⁴ and R¹⁵ may be an alkyl group having less than 15 carbon atoms unsubstituted or at least monosubstituted with CN, CF₃ or a halogen, and at least one CH₂ group may be replaced with —O—, —S—, —C═C—, —OCO—, or —O—CO—. Particular examples of Chemical Formula 37 may be as follows.

In the above compounds, n and m represents 1 to 10 and preferably 1 to 5, o and p are the same or different and independently represents 1 to 10 and preferably 0 to 5, and the sum of o+p is preferably less than 7.

The positive nematic liquid crystal may be a single material or a mixture. In some embodiments, the positive nematic liquid crystal mixture may include,

(a) a liquid crystal component A including at least one compound having a dielectric anisotropy exceeding +1.5;

(b) a liquid crystal component B including at least one compound having a dielectric anisotropy of from −1.5 to +1.5; and

(c) a chiral component C in case of need.

The liquid crystal component A may include at least one compound of Chemical Formula 37. The liquid crystal component B may include at least one compound of Chemical Formula 38. The liquid crystal component B may be the second base liquid crystal molecules.

The component C may include a plurality of commercially available chiral dopants such as cholesteryl nonanoate (CN), S-811, S-1011, S-2011 (Merck KGaA at Darmstadt, Germany and CB15 (BDH Chemicals Ltd., at Poole, England)). The selection of the dopant itself is insignificant.

In Chemical Formula 38, R¹⁶ and R¹⁷ may be the same or different and independently represents an alkyl having less than 15 carbon atoms and unsubstituted or at least monosubstituted with CN, CF₃, or a halogen, in which, at least one CH₂ in the alkyl may be replaced with —O—, —S—, —C≡C—, —CH═CH—, —OC—O— or —OCO—, and the 1,4-phenylene cycle may be independently monosubstituted or polysubstituted with a fluorine.

Ferroelectric Liquid Crystal

The ferroelectric liquid crystal may illustrate a spontaneous polarization in the absence of an electric field and may be a kind of electrically insulating dielectric materials. Different from common dielectric materials, the ferroelectric liquid crystal illustrates a nonproportional spontaneous polarization to the electric field, and the relation between the polarity of the ferroelectric liquid crystal and the electric field illustrates an ideality having an electric hysteresis. The ferroelectric liquid crystal has a particular spontaneous polarization and has a polarization reversal phenomenon of the spontaneous polarization by an electric field.

In some embodiments, the ferroelectric liquid crystal may include ferroelectric liquid crystal molecules. In one aspect, the ferroelectric liquid crystal molecules may be a single material. In other aspects, the ferroelectric liquid crystal molecules may be a mixture of different kinds. For example, the ferroelectric liquid crystal molecules may include a first ferroelectric liquid crystal molecule and a second ferroelectric liquid crystal molecule. In this case, the second ferroelectric liquid crystal molecule may be different from the first ferroelectric liquid crystal molecule.

In other embodiments, the ferroelectric liquid crystal may include the ferroelectric liquid crystal molecules and the third base liquid crystal molecules. Each of the third base liquid crystal molecules may include at least one of a liquid crystal molecule having a negative dielectric anisotropy, a liquid crystal molecule having a positive dielectric anisotropy, and a neutral liquid crystal molecule. In one aspect, the ferroelectric liquid crystal may include one kind of the ferroelectric liquid crystal molecules and the third base molecules. In other aspect, the ferroelectric liquid crystal may include different kinds of the ferroelectric liquid crystal molecules and the third base molecules.

Hereinafter, example embodiments on the ferroelectric liquid crystal may be explained. The following materials may be used alone or as a mixture type.

The ferroelectric liquid crystal may be chiral. For example, the ferroelectric liquid crystal may include a fluorine chiral end ferroelectric liquid crystal, a chiral allyl ester ferroelectric liquid crystal, a center core polyring chiral ferroelectric liquid crystal, a smectic chiral ferroelectric liquid crystal, etc. The ferroelectric liquid crystal may be a banana shape ferroelectric liquid crystal. The ferroelectric liquid crystal may use the fluorine chiral end ferroelectric liquid crystal, the chiral allyl ester ferroelectric liquid crystal, the center core polyring chiral ferroelectric liquid crystal, the smectic chiral ferroelectric liquid crystal, and the banana shape ferroelectric liquid crystal, alone or as a mixture thereof. In addition, the ferroelectric liquid crystal may further include the third base liquid crystal molecules.

The fluorine chiral end ferroelectric liquid crystal may be represented by following Chemical Formula 39.

In Chemical Formula 39, X⁴, X⁵, X⁶ and X⁷ independently represents CF₃, CF₂H, CFH₂, a halogen, an alkyl or an alkoxy, C and D independently represents phenyl, mono-fluorophenyl, di-fluorophenyl, or cyclo-hexyl, E independently represents a single bond, COO, OOC, and C≡C, in which, at least one of E is a single bond, q is 0 or 1, and R¹⁸ represents an end group of following Chemical Formula 40.

In Chemical Formula 40, Z represents O, (CH₂)₁O, or (CH₂)₂O, J and M independently represents hydrogen or an alkyl having 1 to 15 carbon atoms, W represents a linear or branched alkyl chain having 1 to 15 carbon atoms, J, M and W are different from each other, and R¹⁹ represents an alkenyl, an alkenyloxy, an alkynyl, or an alkynoxy having 1 to 15 carbon atoms.

The chiral allyl ester ferroelectric liquid crystal may be represented by Chemical Formula 41.

In Chemical Formula 41, R_(a) and R_(b) independently represents an alkyl having 1 to 20 carbon atoms, Q represents —C(═O)O— or —OC(═O)—, Z represents a fluorine containing alkyl or a halogen substituted alkyl group, and * represents a chiral carbon. Particular examples of Chemical Formula 41 includes 4′-n-(octyloxyphenyl 4′-(1,1,1-trifluoro-2-octyloxycarbonyl)biphenyl-4-carboxylate).

The center core polyring chiral ferroelectric liquid crystal may be represented by following Chemical Formulae 42 to 44.

The compound of Chemical Formula 42 represents S-4-(trans-4-heptylcyclohexyl)-3′-chloro-4″-(1-methylheptyloxy)terphenyl.

The compound of Chemical Formula 43 represents R-4-octyl-3″-chloro-4′″-(1-methylhexyloxy)quarterphenyl.

The compound of Chemical Formula 44 represents S-4-nonyl-3′-fluoro-4″-(2-chloropropyloxy)quarterphenyl.

The compound of Chemical Formula 45 represents S-2-(4-octyl-2′-fluoro-3″-trifluoromethyl-4′″-quarterphenyloxy)-propionate.

The smectic chiral ferroelectric liquid crystal may be represents by at least one of Chemical Formulae 46 and 47.

In Chemical Formulae 46 and 47, each of R²⁰ and R²¹ represents different linear alkyl group having 1 to 9 carbon atoms, R²² and R²³ are the same or different and represent a linear alkyl having 1 to 18 carbon atoms (In R²⁰ to R²³, hydrogen may be substituted with CN, CF₃, or a halogen atom, and —CH₂— group may be optionally substituted with —CH═CH—, —O—, —CO—, —COO—, —OOC—, —O—OC—O— or —S—), and X represents hydrogen or a halogen. Particular examples of Chemical Formulae 46 and 47 are as follows.

The smectic chiral ferroelectric liquid crystal may be represents by Chemical Formula 48.

In Chemical Formula 48, R²⁴ represents a chiral or an achiral alkyl or alkenyl having 1 to 20 carbon atoms, R²⁵ represents a chiral or an achiral alkoxy, alkenyloxy, alkylcarbonyloxy(alkyl-COO—) or alkenylcarbonyloxy(alkenyl-COO—) having 1 to 20 carbon atoms (in R²⁴ and R²⁵, hydrogen may be substituted with CN, CF₃, or a halogen atom, and —CH₂— group may be substituted with —CH═CH—, —O—, —CO—, —COO—, —OOC—, —O—OC—O— or —S—), Z¹ represents a single bond, —COO— or —OOC—, —CH₂CH₂—, —CH═CH—, —C≡C—, —OCH₂— or —CH₂O—, L¹⁰ to L¹⁴ represent hydrogen, a halogen, a cyano, a nitro, or an alkyl or an alkenyl having 1 to 20 carbon atoms (—CH₂— group may be substituted with —CH═CH—, —O—, —CO—, —COO—, —OOC—, —O—OC—O— or —S—), and X⁹ represents —CH— or nitrogen. A particular example of Chemical Formula 48 is as follows.

The banana shape ferroelectric liquid crystal may be represented by following Chemical Formula 49.

In Chemical Formula 49, A¹ represents

B1 represents —N═CH— or —OOC—, R²⁶ and R²⁷ independently represent hydrogen or a halogen, and R²⁸ and R²⁹ independently represents an alkyl or an alkoxy having 8 to 16 carbon atoms. Particular examples of Chemical Formula 49 are as follows.

The ferroelectric liquid crystal may be a single material of the ferroelectric liquid crystal or a mixture including the ferroelectric liquid crystal.

In Chemical Formula 50, X¹⁰ represents hydrogen (H), R³⁰ represents hydrogen or an alkyl having 1 to 15 carbon atoms, R³¹ represents hydrogen, a halogen, or an alkyl group or an alkenyl group having 1 to 20 carbon atoms (in which, one or two —CH₂— groups may be independently replaced with —O—, —C(═O)O— or —Si(CH₃)₂—, one or more hydrogen in the alkyl or the alkenyl group may be replaced with fluorine or CH₃), and each of R³², R³³, R³⁴ and R³⁵ represents CH₃.

When an external electric field is applied to the liquid crystal composition according to the present inventive concept, an induced dipole may become in parallel with the electric field, and a negative nematic liquid crystal may be alignment in a vertical direction to the electric field. Since the alignment characteristic between molecules and the alignment characteristic according to the electric field are strong for the ferroelectric liquid crystal in the liquid crystal composition, the alignment of the liquid crystal composition may become homogeneous and stable.

In accordance with example embodiments, the liquid crystal composition may further include a reactive mesogen material. The liquid crystal composition may include about 0.01 wt % to about 3 wt % of the reactive mesogen material and about 70 wt % to about 99.9 wt % of the negative nematic liquid crystal. The liquid crystal composition may include about 0.01 wt % to about 3 wt % of the reactive mesogen material, about 0.1 wt % to about 30 wt % of a mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal, and a remaining amount of the negative nematic liquid crystal.

The reactive mesogen material represents a polymerizable mesogen compound. “Mesogen compound” or “mesogen material” may include a material or a compound including a mesogen group having a rod shape, a plate shape or a disc shape, and possibly inducing a liquid crystalline phase behavior. The reactive mesogen material may be polymerized by a light such as ultraviolet and may be a material aligning in accordance with the aligned state of a neighboring material.

Examples on the reactive mesogen material may include the compounds represented by the following structure:

P1-A1-(Z1-A2)n-P2

In the structure, P1 and P2 represent at least one among an acrylate group, a methacrylate group, a vinyl group, a vinyloxy group and an epoxy group. A1 and A2 represent at least one among 1,4-phenylene group and naphthalene-2,4-diyl group. Z1 may be one of COO—, OCO— and a single bond, and n may be one of 0, 1 and 2.

More particularly, the structure may include the compounds represented by the following structures.

In the structures, P1 and P2 may include at least one of an acrylate group, a methacrylate group, a vinyl group, a vinyloxy group and an epoxy group.

In example embodiments, the liquid crystal composition includes the ferroelectric liquid crystal along with the nematic liquid crystal, and so, the alignment of the liquid crystal composition may be homogenized and the alignment stability may be improved. In addition, since the liquid crystal composition includes the reactive mesogen material, the aligning velocity of the liquid crystal composition may be increased and the alignment angle may be increased to improve the optical characteristic of the liquid crystal composition.

Liquid Crystal Composition Second Embodiment

The liquid crystal composition in accordance with example embodiments of the present inventive concept may include a non-ferroelectric liquid crystal and a ferroelectric liquid crystal.

In one embodiment of the inventive concept, the non-ferroelectric liquid crystal may include a negative nematic liquid crystal. In this case, the amount of the ferroelectric liquid crystal may be about 0.1 wt % to about 30 wt % based on the total amount of the liquid crystal composition. When the amount of the ferroelectric liquid crystal is about 0.1 wt % or less based on the total amount of the liquid crystal composition, the alignment of the liquid crystal composition may become unstable. When the amount of the ferroelectric liquid crystal exceeds about 30 wt % of the total amount of the liquid crystal composition, the viscosity of the liquid crystal composition may be increased and the response time of a display device including the liquid crystal composition may be decreased. Preferably, the amount of the ferroelectric liquid crystal may be about 10 wt % of the total amount of the liquid crystal composition.

In one aspect, the liquid crystal composition may further include a reactive mesogen material. In this case, the liquid crystal composition may include about 0.1 wt % to about 30 wt % of the ferroelectric liquid crystal, about 0.01 wt % to about 3 wt % of the reactive mesogen material and the remaining amount of the negative nematic liquid crystal.

The constituting elements, structure and examples of the negative nematic liquid crystal, the ferroelectric liquid crystal and the reactive mesogen material may be substantially the same as described above, and detailed description thereabout will be omitted.

In accordance with other example embodiments in the inventive concept, the non-ferroelectric liquid crystal may include a positive nematic liquid crystal and a negative nematic liquid crystal. In this case, the liquid crystal composition may include about 70 wt % to about 99.9 wt % of the negative nematic liquid crystal. The liquid crystal composition may further include about 0.1 wt % to about 30 wt % of a mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal.

The mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal may include about 1 wt % to about 90 wt % of the positive nematic liquid crystal and about 10 wt % to about 99 wt % of the ferroelectric liquid crystal.

In one aspect, the liquid crystal composition may further include a reactive mesogen material. In this case, the liquid crystal composition may include about 0.1 wt % to about 30 wt % of the mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal, about 0.01 wt % to about 3 wt % of the reactive mesogen material and the remaining amount of the negative nematic liquid crystal.

The constituting elements, structure and examples of the negative nematic liquid crystal, the positive nematic liquid crystal, the ferroelectric liquid crystal and the reactive mesogen material may be substantially the same as described above, and detailed description thereabout will be omitted.

In example embodiments, the liquid crystal composition includes the ferroelectric liquid crystal along with the non-ferroelectric liquid crystal, and so, the alignment of the liquid crystal composition may be homogenized and the alignment stability may be improved. In addition, since the liquid crystal composition includes the reactive mesogen material, the aligning velocity of the liquid crystal composition may be increased and the alignment angle may be increased to improve the optical characteristic of the liquid crystal composition.

(Method of Preparing Liquid Crystal Composition)

According to example embodiments of the inventive concept, the liquid crystal composition may be prepared by mixing a negative nematic liquid crystal, a positive nematic liquid crystal and a ferroelectric liquid crystal. The liquid crystal composition may be prepared by mixing about 70 wt % to about 99.9 wt % of the negative nematic liquid crystal, and about 0.1 wt % to about 30 wt % of a mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal. The mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal may be prepared by mixing about 1 wt % to about 90 wt % of the positive nematic liquid crystal and about 10 wt % to about 99 wt % of the ferroelectric liquid crystal.

In one aspect, the liquid crystal composition may further include a reactive mesogen material. In this case, the liquid crystal composition may be prepared by mixing about 0.01 wt % to about 3 wt % of the reactive mesogen material, about 0.1 wt % to about 30 wt % of the mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal, and the remaining amount of the positive nematic liquid crystal.

According to other example embodiments of inventive concept, the liquid crystal composition may be prepared by mixing the negative nematic liquid crystal and the ferroelectric liquid crystal. More particularly, the liquid crystal composition may be prepared by mixing about 70 wt % to about 99.9 wt % of the negative nematic liquid crystal, and about 0.1 wt % to about 30 wt % of the ferroelectric liquid crystal.

In one aspect, the liquid crystal composition may further include a reactive mesogen material. In this case, the liquid crystal composition may be prepared by mixing about 0.01 wt % to about 3 wt % of the reactive mesogen material, about 0.1 wt % to about 30 wt % of the ferroelectric liquid crystal, and the remaining amount of the negative nematic liquid crystal.

A processing temperature while conducting a mixing process may be set to a temperature at which the largest amount of the material in the liquid crystal composition illustrates an isotropic property. In example embodiments, the mixing process may be conducted at a temperature range of about 90° C. to about 100° C. The temperature range may be set to a temperature range at which the nematic negative liquid crystal illustrates the isotropic property. In example embodiments, the mixing of the liquid crystals are conducted at about 90° C. to about 100° C., however, the temperature range may not limited to the range in the present inventive concept.

Hereinafter, the electric properties of the thus prepared liquid crystal composition will be described.

FIG. 1 is a graph illustrating an electric characteristic of a liquid crystal composition in accordance with an example embodiment. In FIG. 1, the x-axis represents time in seconds, and the y-axis represents an applied voltage in volts (V).

When a voltage is applied to the liquid crystal composition prepared by the above described method, a peak that may not be illustrated in a liquid crystal composition including only the nematic liquid crystal may be illustrated as in FIG. 1. This peak is illustrated by the ferroelectric liquid crystal. Accordingly, the nematic liquid crystal and the ferroelectric liquid crystal in the liquid crystal composition may be present in a mixture state but may not be in a compound state. Thus, the nematic liquid crystal may illustrate the inherent property thereof, and the ferroelectric liquid crystal may illustrate the inherent property thereof. Therefore, the nematic liquid crystal and the ferroelectric liquid crystal may reinforce and/or interfere in the behavior of each other.

(Liquid Crystal Display Device)

FIG. 2 is a cross-sectional view for explaining a liquid crystal display device in accordance with an example embodiment.

Referring to FIG. 2, a liquid crystal display device may include a first displaying plate 100, a second displaying plate 200 facing the first displaying plate 100 with a constant distance, and a liquid crystal layer 300 disposed between the first and second displaying plates 100 and 200.

The first displaying plate 100 may include a first substrate 110, a first electrode 120 and a first alignment layer 170. The first substrate 110, the first electrode 120 and the first alignment layer 170 may be integrated one by one.

The first electrode 120 may include a transparent conductive material, for example, indium tin oxide (ITO), or indium zinc oxide (IZO). In example embodiments, the first electrode 120 may include a first slit formed by patterning a portion of the first electrode 120.

The first alignment layer 170 may include an alignment base material and a reactive mesogen material. The alignment base material of the first alignment layer may include at least one of polyimide, polyvinyl alcohol (PVA), polystyrene, and nylon. In addition, the examples of the reactive mesogen material are substantially the same as described above and so, detailed description thereabout will be omitted. In other embodiments, the first alignment layer 170 may be omitted.

The second displaying plate 200 may include a second substrate 210, a second electrode 220 and a second alignment layer 270. The second substrate 210, the second electrode 220 and the second alignment layer 270 may be integrated one by one. The first and second displaying plates 100 and 200 may be disposed with a distance so that the first and second alignment layers 170 and 270 may face each other.

The second electrode 220 may include the same or similar material as the first electrode 120, and may be provided with a different voltage from that into the first electrode 120. In example embodiments, the second electrode 220 may include a second slit formed by patterning a portion of the second electrode 220.

The second alignment layer 270 may include an alignment base material and a reactive mesogen material. The alignment base material of the second alignment layer 270 may be similar to or substantially the same as the alignment base material of the first alignment layer. The examples of the reactive mesogen material may be substantially the same as described above, and the explanation thereabout will be omitted. In other embodiments, the second alignment layer 270 may be omitted.

The liquid crystal layer 300 may be disposed between the first and second displaying plates 100 and 200. The liquid crystal layer 300 may include the above described liquid crystal composition, and detailed description will be referred to the above explanation.

In example embodiments, each of the first and second electrodes 120 and 220 are disposed on each of the first and second displaying plates 100 and 200. However, the first and second electrodes 120 and 220 may be disposed on one of the first and second displaying plates 100 and 200. In addition, the first and second electrodes 120 and 220 may be disposed on the same floor, or the first and second electrodes 120 and 220 may be disposed on different floors with an interposing insulating layer. In addition, the first and second slits may be formed on one of the first and second electrodes 120 and 220.

FIG. 3 is a plan view for explaining slit phenomenon of electrodes in accordance with example embodiments.

Referring to FIG. 3, at least one electrode among the first and second electrodes 120 and 220 may have a chevron pattern. The chevron pattern may have a V shape including a first straight line extended in a first direction and a second straight line extended in a second direction crossing the first direction.

In example embodiments, the first slit and the second slit having the chevron pattern are illustrated, however, the structure of the first and second slits may not be limited to the chevron structure in the present inventive concept.

Hereinafter, the present inventive concept will be described in more detail referring to examples and comparative examples. The inventive concept may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein.

Liquid Crystal Display Device Example 1

A liquid crystal display device including a first displaying plate including a first substrate and a first electrode having a first slit of a chevron pattern, a second displaying plate including a second substrate and a second electrode having a second slit of the chevron pattern, and a liquid crystal layer filling up the space between the first and second displaying plates was manufactured. The liquid crystal display device was manufactured in a patterned vertical alignment (PVA) mode.

The liquid crystal layer was manufactured by using a liquid crystal composition prepared by mixing at 100° C. of 90 wt % of MLC 6608 (Δn=0.084, ∈=−4.3) purchased by Merck Co., and 10 wt % of KFLC 3 (Δn=0.18) purchased by Kingston Chemical Co. The thickness of the liquid crystal layer of the liquid crystal display device was 3.8 μm.

Examples 2 to 4

Liquid crystal display devices in accordance with examples 2 to 4 were manufactured by conducting the same procedure described in Example 1 except for the thickness of the liquid crystal layer. The thickness of the liquid crystal layer in Examples 2 to 4 is illustrated in following Table 1.

Example 5

A liquid crystal display device including a first displaying plate including a first substrate and a first electrode having a first slit of a chevron pattern, a second displaying plate including a second substrate and a second electrode having a second slit of the chevron pattern, and a liquid crystal layer filling up the space between the first and second displaying plates was manufactured. The liquid crystal display device was manufactured in a PVA mode.

The liquid crystal layer was manufactured by using a liquid crystal composition prepared by mixing at 100° C. of 99 wt % of MLC 6608 (Δn=0.084, ∈=−4.3) purchased by Merck Co., and 1 wt % of KFLC 3 (Δn=0.18) purchased by Kingston Chemical Co. The thickness of the liquid crystal layer of the liquid crystal display device was 4.3 μm.

Examples 6 to 8

Liquid crystal display devices in accordance with examples 6 to 8 were manufactured by conducting the same procedure described in Example 5 except for the mixing ratio of MLC 6608 and KFLC 3 in the liquid crystal layer. The mixing ratio of MLC 6608 and KFLC 3 in the liquid crystal layer is illustrated in following Table 1.

Example 9

A liquid crystal display device including a first displaying plate including a first substrate and a first electrode having a first slit of a chevron pattern, a second displaying plate including a second substrate and a second electrode having a second slit of the chevron pattern, and a liquid crystal layer filling up the space between the first and second displaying plates was manufactured. The liquid crystal display device was manufactured in a PVA mode.

The liquid crystal layer was manufactured by using a liquid crystal composition prepared by mixing at 100° C. of 90 wt % of MLC 6608 (Δn=0.084, ∈=−4.3) purchased by Merck Co., 5 wt % of ZKC-5085 (Δn=0.16, E=12) purchased by Chisso Co., and 5 wt % of KFLC 3 (Δn=0.18) purchased by Kingston Chemical Co. The thickness of the liquid crystal layer of the liquid crystal display device was 4.3 μm.

Comparative Example 1

A liquid crystal display device including a first displaying plate including a first substrate and a first electrode having a first slit of a chevron pattern, a second displaying plate including a second substrate and a second electrode having a second slit of the chevron pattern, and a liquid crystal layer filling up the space between the first and second displaying plates was manufactured. The liquid crystal display device was manufactured in a PVA mode.

The liquid crystal layer was manufactured by using 100 wt % of MLC 6608 (Δn=0.084, E=−4.3) purchased by Merck Co. The thickness of the liquid crystal layer of the liquid crystal display device was 4.3 μm.

Comparative Examples 2 and 3

Liquid crystal display devices in accordance with Comparative Examples 2 and 3 were manufactured by conducting the same procedure described in Comparative Example 1 except for the thickness of the liquid crystal layer. The thickness of the liquid crystal layer in Comparative Examples 2 and 3 is illustrated in following Table 1.

TABLE 1 Liquid crystal layer MLC 6608 [wt %] KFLC 3 [wt %] ZKC-5085 [wt %] (negative nematic (ferroelectric (positive nematic Thickness of liquid liquid crystal) liquid crystal) liquid crystal) crystal layer [μm] Example 1 90 10 0 3.8 Example 2 90 10 0 4.0 Example 3 90 10 0 4.3 Example 4 90 10 0 4.5 Comparative 100 0 0 4.3 Example 1 Comparative 100 0 0 4.5 Example 2 Comparative 100 0 0 4.8 Example 3 Example 5 99 1 0 4.3 Example 6 95 5 0 4.3 Example 7 80 20 0 4.3 Example 8 70 30 0 4.3 Example 9 90 5 5 4.3

Evaluation on Transmittance

FIGS. 4A to 4E are graphs illustrating the transmittance of liquid crystal display devices in accordance with Examples 1 to 4 and Comparative Examples 1 to 3.

FIGS. 4A to 4C are graphs illustrating the transmittance of the liquid crystal display devices with respect to the applied voltages. In FIGS. 4A to 4C, the x-axis represents an applied voltage in voltage units [V], and the y-axis represents the transmittance.

Referring to FIG. 4A, the liquid crystal display devices according to Examples 1 to 4 illustrate better transmittance property over all than those according to Comparative Examples 1 to 3. More particularly, FIG. 4B selectively illustrates the transmittance of the liquid crystal display devices according to Example 4 and Comparative Example 2 in FIG. 4A. Referring to FIG. 4B, the transmittance for Example 4 is higher than the transmittance for Comparative Example 2 with the same thickness condition of the liquid crystal layer of 4.5 μm. FIG. 4C selectively illustrates the transmittance of the liquid crystal display devices according to Example 4 and Comparative Example 3 in FIG. 4A. Referring to FIG. 4C, the transmittance for Example 4, which illustrates the best transmittance among Examples 1 to 4, is higher than the transmittance for Comparative Example 3, which illustrates the best transmittance among Comparative Examples 1 to 3.

FIGS. 4D and 4E are graphs illustrating the transmittance with respect to the thickness of the liquid crystal layer after applying the voltage of 7V to the liquid crystal display devices according to Examples 1 to 4 and the liquid crystal display devices according to Comparative Example 1 to 3. More particularly, FIG. 4D is a graph illustrating the transmittance with respect to the thickness of the liquid crystal layer, and FIG. 4E is a graph illustrating the transmittance with respect to the multiplied product (Δn·d) of the thickness (d) of the liquid crystal layer and the refractive index (Δn) of the liquid crystal layer. In FIGS. 4D and 4E, the x-axis represents the length in μm unit, and the y-axis represents the transmittance.

Referring to FIG. 4D, the transmittance of the liquid crystal display devices according to Examples 1 to 4 is higher than that according to Comparative Examples 1 to 3 by about 17% to about 30%. Referring to FIG. 4E, when examining the transmittance according to Δn·d, the transmittance of the liquid crystal display devices according to Examples 1 to 4 is higher than that according to Comparative Examples 1 to 3 by about 9% to about 17%.

As evaluated above, since the ferroelectric liquid crystal in the liquid crystal layer according to Examples 1 to 4 induces the homogeneous and stable alignment of liquid crystal molecules, the transmittance of the liquid crystal display devices according to Examples 1 to 4 is confirmed to be higher than the transmittance of the liquid crystal display devices according to Comparative Examples 1 to 3.

Evaluation on Response Time

FIGS. 5A to 5D are graphs illustrating the response time of liquid crystal display devices in accordance with Examples 1 to 4 and Comparative Examples 1 to 3.

FIGS. 5A and 5B are graphs illustrating the response time according to an applied voltage. In FIGS. 5A and 5B, the x-axis represents the applied voltage in volts [V], and the y-axis represents the response time.

Referring to FIG. 5A, the response time of the liquid crystal display devices according to Examples 1 to 4 is not much slower than the response time of the liquid crystal display devices according to Comparative Examples 1 to 3. Since the liquid crystal layer includes the ferroelectric liquid crystal in Examples 1 to 4, the viscosity of the liquid crystal layer may be increased. Thus, the response time of the liquid crystal devices of Examples 1 to 4 may become slightly lower than or similar value to the response time of the liquid crystal display devices according to Comparative Examples 1 to 3.

In FIG. 5B, the response time according to Example 3, which illustrates the best transmittance among Examples 1 to 4, and Comparative Example 3, which illustrates the best transmittance among Comparative Examples 1 to 3, with respect to the voltage are selectively illustrated. Referring to FIG. 5B, when comparing the response time of Example 3 illustrating a good transmittance and Comparative Example 3, the response time of Example 3 is confirmed to be faster than the response time of Comparative Example 3.

FIGS. 5C and 5D are graphs illustrating the response time according to the thickness of the liquid crystal layer of the liquid crystal display devices according to Examples 1 to 4 and Comparative Examples 1 to 3 after applying the voltage of 7V. More particularly, FIG. 5C is a graph illustrating the response time according to the thickness of the liquid crystal layer, and FIG. 5D is a graph illustrating the response time with respect to the multiplied product (Δn·d) of the thickness (d) of the liquid crystal layer and the refractive index (Δn) of the liquid crystal layer. In FIGS. 5C and 5D, the x-axis represents the length in [μm] unit, and the y-axis represents the response time in [ms] unit.

Referring to FIG. 5C, the response time of the liquid crystal display device of Example 1 having a liquid crystal layer having a thickness of about 3.8 μm is about 18 ms, and the thickness of the liquid crystal layer of the liquid crystal display device according to Comparative Examples is required to be at least 4.3 μm to illustrate the response time of about 18 ms. Referring to FIG. 5D, when examining the response time according to Δn·d, the response time of the liquid crystal display devices according to Examples 1 to 4 is increased by about 22% to about 24% than the response time of the liquid crystal display devices according to Comparative Examples 1 to 3.

As shown from the results of the response time obtained by multiplying the thickness of the liquid crystal layer and the refractive index of the liquid crystal layer, the liquid crystal display devices according to Examples 1 to 4 illustrate faster response time than the liquid crystal display devices according to Comparative Examples 1 to 3 by forming the liquid crystal layer having an appropriate thickness and refractive index, even though the liquid crystal layer of Examples 1 to 4 include the ferroelectric liquid crystal having a relatively high viscosity. Thus, the liquid crystal display devices according to Examples 1 to 4 illustrate a fast response time and a stable and homogeneous alignment of the liquid crystal molecules because of the ferroelectric liquid crystal.

Evaluation on Transmittance and Response Time According to Amount of Ferroelectric Liquid Crystal

FIG. 6A is a graph illustrating the transmittance of liquid crystal display devices in accordance with Examples 5 to 8, and FIG. 6B is a graph illustrating the response time of liquid crystal display devices in accordance with Examples 5 to 8.

Referring to FIG. 6A, the transmittance is found to be increased when the amount of the ferroelectric liquid crystal in the liquid crystal layer is increased. However, referring to FIG. 6B, the response time is found to be decreased by two times when the amount of the ferroelectric liquid crystal in the liquid crystal layer is increased. Thus, the amount of the ferroelectric liquid crystal in the liquid crystal composition in the embodiments of inventive concept is preferably controlled so as not to exceed about 30 wt % based on the total amount of the liquid crystal composition.

Texture Evaluation

FIGS. 7A to 7C and FIGS. 8A to 8C are textures of liquid crystal display devices in accordance with Comparative Example 1, and Examples 3 and 9.

The liquid crystal display devices in Comparative Example 1, Example 3 and Example 9 are substantially the same except for the component ratios in the liquid crystal layer. For the convenience of the explanation, the component ratios in the liquid crystal layer are illustrated in Table 2.

TABLE 2 Liquid crystal layer MLC 6608 [wt %] KFLC 3 [wt %] ZKC-5085 [wt %] Thickness (negative nematic (ferroelectric (positive nematic of liquid crystal liquid crystal) liquid crystal) liquid crystal) layer [μm] Comparative 100 0 0 4.3 Example 1 Example 3 90 10 0 4.3 Example 9 90 5 5 4.3

After applying the voltage of 7V onto the liquid crystal display devices according to Comparative Example 1, Examples 3 and Example 9, a cross polarizing plate was rotated to obtain white images and black images.

The textures in FIGS. 7A to 7C are white images under the cross polarizing plate. More particularly, the white images are obtained when the angle between the cross polarizing plate and the liquid crystal molecules in the liquid crystal layer is 45°. The bright images may be illustrated through the penetration of the light through the liquid crystal layer. This phenomenon may be confirmed in following Equation 1.

$\begin{matrix} {T = {\frac{1}{2}{\sin^{2}\left( {2\varphi} \right)}{\sin^{2}\left( \frac{{\pi\Delta}\; n*d}{\lambda} \right)}}} & {\langle{{Equation}\mspace{14mu} 1}\rangle} \end{matrix}$

In Equation 1, T represents transmittance, Φ represents an angle between a polarization plate and a liquid crystal molecule, Δn represents a double refractive index, d represents the thickness of a liquid crystal layer, and λ, represents the wavelength of an incident light. In Equation 1, when Φ is 45°, the value of sin² is the highest value with the highest transmittance.

FIGS. 7A to 7C are textures of Comparative Example 1, Example 3 and Example 9. Referring to FIG. 7A, defects of black looking at the edge portions of the slits or at the borders of the slits are found. Referring to FIG. 7B, the defects at the edge portions of the slits are found to decrease when comparing with those in FIG. 7A. Referring to FIG. 7C, the defects at the edge portions of the slits and at the borders of the slits are found to be removed.

The textures in FIGS. 8A to 8C are black images under a cross polarizing plate. More particularly, the black images are obtained when the angle between the cross polarizing plate and the liquid crystal molecules in the liquid crystal layer is 0°. Since a rotated upper polarizing plate has a perpendicular polarization to the polarized light passed through the liquid crystal layer, the black images may be illustrated. In Equation 1, when Φ is 0°, the value of sin² is 0, and the transmittance becomes 0.

FIGS. 8A to 8C are textures in Comparative Example 1, Example 3 and Example 9. Referring to FIG. 8A, light leaking phenomenon is found at the edge portions of the slits and at the borders of the slits. Referring to FIGS. 8B and 8C, lots of the light leaking phenomenon at the edge portions of the slits and at the borders of the slits is found to be removed when comparing with that in FIG. 8A.

When examining the textures, the alignment of the liquid crystal molecules in the liquid crystal layer including the ferroelectric material is homogeneous and stable when comparing with the liquid crystal layer excluding the ferroelectric material, and the luminance of the liquid crystal display device may be increased.

FIGS. 9A and 9B are graphs illustrating the gray level of the textures in Comparative Example 3, Example 3 and Example 9. FIGS. 9A and 9B may be estimated by 256 (2⁸) gray levels. Gray approaches to black when the gray level approaches to 0, and the concentration of the gray may be illustrated by levels from 0 to 256.

FIG. 9A illustrates the gray level of the textures in FIGS. 7A to 7C and illustrates lots of white images near the gray level of 256. The texture in FIG. 7A according to Comparative Example 1 is found a lot in the gray level of about 200 to 230 and illustrates a large peak width. The texture in FIG. 7B according to Example 3 is found a lot in the gray level of about 240 to 250 and illustrates a smaller peak width than that of Comparative Example 1. The texture in FIG. 7C according to Example 9 is found a lot in the gray level of about 230 to 250 and illustrates a smaller peak width than that of Comparative Example 1.

FIG. 9B illustrates the gray level of the textures in FIGS. 8A to 8C and illustrates lots of black images near the gray level of 0. The texture in FIG. 8A according to Comparative Example 1 is found a lot in the gray level of about 30 to 50 and illustrates a large peak width. The texture in FIG. 8B according to Example 3 is found a lot in the gray level of about 0 to 20 and illustrates a smaller peak width than that of Comparative Example 1. The texture in FIG. 8C according to Example 9 is found a lot in the gray level of about 0 to 30 and illustrates a smaller peak width than that of Comparative Example 1.

When examining the graphs in FIGS. 9A and 9B, the alignment of the liquid crystal molecules in the liquid crystal layer including the ferroelectric material is homogeneous and stable when comparing with the liquid crystal layer excluding the ferroelectric material, and the luminance of the liquid crystal display device may be increased.

The above-disclosed subject matter is to be considered illustrative and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the inventive concept. Thus, to the maximum extent allowed by law, the scope of the inventive concept is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description. 

What is claimed is:
 1. A liquid crystal composition comprising: a negative nematic liquid crystal; a positive nematic liquid crystal; and a ferroelectric liquid crystal.
 2. The liquid crystal composition of claim 1, wherein the liquid crystal composition comprises: about 70 to about 99.9 wt % of the negative nematic liquid crystal; and about 0.1 to about 30 wt % of a mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal.
 3. The liquid crystal composition of claim 2, wherein an amount of the ferroelectric liquid crystal is about 10 to about 99 wt % based on the mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal.
 4. The liquid crystal composition of claim 1, further comprising a reactive mesogen material.
 5. The liquid crystal composition of claim 4, wherein the liquid crystal composition comprises: about 0.1 to about 30 wt % of the mixture of the positive nematic liquid crystal and the ferroelectric liquid crystal; about 0.01 to about 3 wt % of the reactive mesogen material; and a remaining amount of the negative nematic liquid crystal.
 6. The liquid crystal composition of claim 1, wherein the negative nematic liquid crystal includes negative nematic liquid crystal molecules.
 7. The liquid crystal composition of claim 6, wherein the negative nematic liquid crystal further includes first base liquid crystal molecules, each of the first base liquid crystal molecules including at least one selected from the group consisting of a negative nematic liquid crystal molecule, a positive nematic liquid crystal molecule, and a neutral liquid crystal molecule.
 8. The liquid crystal composition of claim 6, wherein the negative nematic liquid crystal molecules comprise: a first negative nematic liquid crystal molecule having a first negative dielectric anisotropy; and a second negative nematic liquid crystal molecule having a second negative dielectric anisotropy different from the first negative dielectric anisotropy.
 9. The liquid crystal composition of claim 1, wherein the positive nematic liquid crystal includes positive nematic liquid crystal molecules.
 10. The liquid crystal composition of claim 9, wherein the positive nematic liquid crystal further includes second base liquid crystal molecules, each of the second base liquid crystal molecules including at least one selected from the group consisting of a negative nematic liquid crystal molecule, a positive nematic liquid crystal molecule, and a neutral liquid crystal molecule.
 11. The liquid crystal composition of claim 9, wherein the positive nematic liquid crystal molecules comprise: a first positive nematic liquid crystal molecule having a first positive dielectric anisotropy; and a second positive nematic liquid crystal molecule having a second positive dielectric anisotropy different from the first positive dielectric anisotropy.
 12. The liquid crystal composition of claim 1, wherein the ferroelectric liquid crystal further comprises ferroelectric liquid crystal molecules.
 13. The liquid crystal composition of claim 12, wherein the ferroelectric liquid crystal further comprises third base liquid crystal molecules, each of the third base liquid crystal molecules including at least one selected from the group consisting of a negative nematic liquid crystal molecule, a positive nematic liquid crystal molecule, and a neutral liquid crystal molecule.
 14. The liquid crystal composition of claim 12, wherein the ferroelectric liquid crystal molecules comprise: a first ferroelectric liquid crystal molecule; and a second ferroelectric liquid crystal molecule different from the first ferroelectric liquid crystal molecule.
 15. A liquid crystal composition comprising: a non-ferroelectric liquid crystal; and a ferroelectric liquid crystal.
 16. The liquid crystal composition of claim 15, wherein the liquid crystal composition comprises about 0.1 to about 30 wt % of the ferroelectric liquid crystal.
 17. The liquid crystal composition of claim 15, wherein the non-ferroelectric liquid crystal comprises: a negative nematic liquid crystal; and a positive nematic liquid crystal.
 18. The liquid crystal composition of claim 15, wherein the non-ferroelectric liquid crystal comprises a negative nematic liquid crystal.
 19. The liquid crystal composition of claim 18, wherein the liquid crystal composition comprises: about 70 to about 99.9 wt % of the negative nematic liquid crystal; and about 0.1 to about 30 wt % of the ferroelectric liquid crystal.
 20. The liquid crystal composition of claim 18, further comprising a reactive mesogen material.
 21. The liquid crystal composition of claim 20, wherein the liquid crystal composition comprises: about 0.1 to about 30 wt % of the ferroelectric liquid crystal; about 0.01 to about 3 wt % of the reactive mesogen material; and a remaining amount of the negative nematic liquid crystal. 